Beating the heat: A translation factor and an RNA mobilize the heat shock transcription factor HSF1

Role of HSF1 in cell division, tumorigenesis and therapy: a literature review

Heat shock factor 1 (HSF1) is the master orchestrator of the heat shock response (HSR), a critical process for maintaining cellular health and protein homeostasis. These effects are achieved through rapid expression of molecular chaperones, the heat shock proteins (HSPs), which ensure correct protein folding, repair, degradation and stabilization of multiprotein complexes. In addition to its role in the HSR, HSF1 influences the cell cycle, including processes such as S phase progression and regulation of the p53 pathway, highlighting its importance in cellular protein synthesis and division. While HSF1 activity offers neuroprotective benefits in neurodegenerative diseases, its proteome-stabilizing function may also reinforce tumorigenic transformation. HSF1 overexpression in many types of cancer reportedly enhances cell growth enables survival, alters metabolism, weakens immune response and promotes angiogenesis or epithelial-mesenchymal transition (EMT) as these cells enter a form of "HSF1 addiction". Furthermore, the client proteins of HSF1-regulated chaperones, particularly Hsp90, include numerous key players in classical tumorigenic pathways. HSF1 thus presents a promising therapeutic target for cancer treatment, potentially in combination with HSP inhibitors to alleviate typical initiation of HSR upon their use.

Corticosterone dynamically regulates retrotransposable element expression in the rat hippocampus and C6 cells

The hippocampus is a highly plastic brain region sensitive to environmental stress. It shows dynamic changes in epigenetic marks associated with stress related learning. Previous work has shown that acute stress induces substantial transient changes in histone H3 lysine 9 trimethylation (H3K9me3). Moreover, increased H3K9me3 is enriched in hippocampal gene deserts accumulating within endogenous retroviruses and transposable elements. We have found that in response to acute glucocorticoid treatment, a similar change in global H3K9me3 is observed. However, when localized we found that H3K9me3 is markedly decreased at B2 short interspersed nuclear elements but not within intracisternal-A particle endogenous retroviruses. Further, decreased H3K9me3 valence within B2 elements was associated with increased transcript abundance. These data demonstrate the capacity for acute glucocorticoids to mobilize transposable elements via epigenetic unmasking. Reconciled with previous findings following acute stress, this suggests the capacity for mobile elements to potentially function as novel regulators given their dynamic regulation by stress and glucocorticoids.

Screening of drought-resistance related genes and analysis of promising regulatory pathway in camel renal medulla

Camels as a sort of animal long living in desert have evolved stress-resistance characteristics to adapt to environment with high temperature and water shortage environment. However, the research of non-coding RNA (ncRNA)-mediated molecular regulation about how camel responds to arid condition in post-transcriptional regulation level is deficient. Under water-deprivation stress, by RNA-sequencing of camel renal medulla associated with regulating water metabolism, we detected significantly differential 575 alternative splicing events (ASEs) and 17 mRNAs, 26 miRNAs and 0 lncRNA. The down-regulated ACLY and LOC105061856, up-regulated PCBP2 and miR-195 potentially targeting LOC105061856 and PCBP2 mRNA were selected as candidate resistance-related genes. In quantitative experiment, the expression level of above four genes was consistent with RNA-seq data by qRT-PCR. The suppressive cell dehydration with down-regulated ACLY, inhibitive aerobic respiration with down-regulated LOC105061856 targeted by miR-195 and strong anti-oxidative capability with PCBP2 aimed by miR-195 may be regulatory modes of camel renal medulla adapting to water-deprivation condition.

Transposable Elements

Transposable elements (TEs) are low-complexity elements (e.g., LINEs, SINEs, SVAs, and HERVs) that make up to two-thirds of the human genome. There is mounting evidence that TEs play an essential role in molecular functions that influence genomic plasticity and gene expression regulation. With the advent of next-generation sequencing approaches, our understanding of the relationship between TEs and psychiatric disorders will greatly improve. In this chapter, the Authors comprehensively summarize the state-of the-art of TE research in animal models and humans supporting a framework in which TEs play a functional role in mechanisms affecting a variety of behaviors, including neurodevelopmental, neuropsychiatric, and neurodegenerative disorders. Finally, the Authors discuss recent therapeutic applications raised from the increasing experimental evidence on TE functional mechanisms.

Mechanisms of Hsp90 regulation

Heat shock protein 90 (Hsp90) is a molecular chaperone that is involved in the activation of disparate client proteins. This implicates Hsp90 in diverse biological processes that require a variety of co-ordinated regulatory mechanisms to control its activity. Perhaps the most important regulator is heat shock factor 1 (HSF1), which is primarily responsible for upregulating Hsp90 by binding heat shock elements (HSEs) within Hsp90 promoters. HSF1 is itself subject to a variety of regulatory processes and can directly respond to stress. HSF1 also interacts with a variety of transcriptional factors that help integrate biological signals, which in turn regulate Hsp90 appropriately. Because of the diverse clientele of Hsp90 a whole variety of co-chaperones also regulate its activity and some are directly responsible for delivery of client protein. Consequently, co-chaperones themselves, like Hsp90, are also subject to regulatory mechanisms such as post translational modification. This review, looks at the many different levels by which Hsp90 activity is ultimately regulated.

Regulatory Mechanisms of Hsp90

The ability of Hsp90 to activate a disparate clientele implicates this chaperone in diverse biological processes. To accommodate such varied roles, Hsp90 requires a variety of regulatory mechanisms that are coordinated in order to modulate its activity appropriately. Amongst these, the master-regulator heat shock factor 1 (HSF1) is critically important in upregulating Hsp90 during stress, but is also responsible, through interaction with specific transcription factors (such as STAT1 and Strap/p300) for the integration of a variety of biological signals that ultimately modulate Hsp90 expression. Additionally, transcription factors, such as STAT1, STAT3 (including STAT1-STAT3 oligomers), NF-IL6, and NF-kB, are known to influence Hsp90 expression directly. Co-chaperones offer another mechanism for Hsp90 regulation, and these can modulate the chaperone cycle appropriately for specific clientele. Co-chaperones include those that deliver specific clients to Hsp90, and others that regulate the chaperone cycle for specific Hsp90-client complexes by modulating Hsp90s ATPase activity. Finally, post-translational modification (PTM) of Hsp90 and its co-chaperones helps too further regulate the variety of different Hsp90 complexes found in cells.

FK506 binding protein 51 integrates pathways of adaptation: FKBP51 shapes the reactivity to environmental change

This review portraits FK506 binding protein (FKBP) 51 as "reactivity protein" and collates recent publications to develop the concept of FKBP51 as contributor to different levels of adaptation. Adaptation is a fundamental process that enables unicellular and multicellular organisms to adjust their molecular circuits and structural conditions in reaction to environmental changes threatening their homeostasis. FKBP51 is known as chaperone and co-chaperone of heat shock protein (HSP) 90, thus involved in processes ensuring correct protein folding in response to proteotoxic stress. In mammals, FKBP51 both shapes the stress response and is calibrated by the stress levels through an ultrashort molecular feedback loop. More recently, it has been linked to several intracellular pathways related to the reactivity to drug exposure and stress. Through its role in autophagy and DNA methylation in particular it influences adaptive pathways, possibly also in a transgenerational fashion. Also see the video abstract here.

Thermal sensation and cell adaptability

Whole person adaptive comfort is discussed with reference to recent findings in molecular scale systems biology. The observations are upscaled to hypotheses relating to less traditional interpretations of thermal processes, which have new implications for indoor climate management and design. Arguments are presented for a revision of current focus, model and paradigm. The issue is seen as a problem of integrating theoretical development, conceptual modeling and as an investigation of the extent to which environments and acclimatization can be used to achieve individual fitness and health, not only at the subjective comfort level, as hitherto promoted. It is argued that there are many questions yet to be asked about adaptability before celebrating a particular adaptive state.

Regulation of HSF1 function in the heat stress response: implications in aging and disease

To dampen proteotoxic stresses and maintain protein homeostasis, organisms possess a stress-responsive molecular machinery that detects and neutralizes protein damage. A prominent feature of stressed cells is the increased synthesis of heat shock proteins (Hsps) that aid in the refolding of misfolded peptides and restrain protein aggregation. Transcriptional activation of the heat shock response is orchestrated by heat shock factor 1 (HSF1), which rapidly translocates to hsp genes and induces their expression. Although the role of HSF1 in protecting cells and organisms against severe stress insults is well established, many aspects of how HSF1 senses qualitatively and quantitatively different forms of stresses have remained poorly understood. Moreover, recent discoveries that HSF1 controls life span have prompted new ways of thinking about an old transcription factor. Here, we review the established role of HSF1 in counteracting cell stress and prospect the role of HSF1 as a regulator of disease states and aging.

Heat shock transcription factor 1 localizes to sex chromatin during meiotic repression

Heat shock factor 1 (HSF1) is an important transcription factor in cellular stress responses, cancer, aging, and developmental processes including gametogenesis. Disruption of Hsf1, together with another HSF family member, Hsf2, causes male sterility and complete lack of mature sperm in mice, but the specific role of HSF1 in spermatogenesis has remained unclear. Here, we show that HSF1 is transiently expressed in meiotic spermatocytes and haploid round spermatids in mouse testis. The Hsf1(-/-) male mice displayed regions of seminiferous tubules containing only spermatogonia and increased morphological abnormalities in sperm heads. In search for HSF1 target genes, we identified 742 putative promoters in mouse testis. Among them, the sex chromosomal multicopy genes that are expressed in postmeiotic cells were occupied by HSF1. Given that the sex chromatin mostly is repressed during and after meiosis, it is remarkable that HSF1 directly regulates the transcription of sex-linked multicopy genes during postmeiotic repression. In addition, our results show that HSF1 localizes to the sex body prior to the meiotic divisions and to the sex chromocenter after completed meiosis. To the best of our knowledge, HSF1 is the first known transcription factor found at the repressed sex chromatin during meiosis.

Evidence for bacterial origin of heat shock RNA-1

The heat shock RNA-1 (HSR1) is a noncoding RNA (ncRNA) reported to be involved in mammalian heat shock response. HSR1 was shown to significantly stimulate the heat-shock factor 1 (HSF1) trimerization and DNA binding. The hamster HSR1 sequence was reported to consist of 604 nucleotides (nt) plus a poly(A) tail and to have only a 4-nt difference with the human HSR1. In this study, we present highly convincing evidence for bacterial origin of the HSR1. No HSR1 sequence was found by exhaustive sequence similarity searches of the publicly available eukaryotic nucleotide sequence databases at the NCBI, including the expressed sequence tags, genome survey sequences, and high-throughput genomic sequences divisions of GenBank, as well as the Trace Archive database of whole genome shotgun sequences, and genome assemblies. Instead, a putative open reading frame (ORF) of HSR1 revealed strong similarity to the amino-terminal region of bacterial chloride channel proteins. Furthermore, the 5' flanking region of the putative HSR1 ORF showed similarity to the 5' upstream regions of the bacterial protein genes. We propose that the HSR1 was derived from a bacterial genome fragment either by horizontal gene transfer or by bacterial infection of the cells. The most probable source organism of the HSR1 is a species belonging to the order Burkholderiales.